<html>
<meta charset="utf-8">

<head>
    <script src="jquery-3.2.1.min.js"></script>
    <script>
      function invoke(){
          $('#frm_child').contents().find('#btn_show').click();
      }
      function getselect(){
          var collction=$('input[type=radio]');
          $.each(collction,function(i,item){
              //alert(collction[i].checked);
              if(item.checked){
                  alert(i)
              }
          });
      }
      function isExit(){
          var a=$('#ttttt');
          if(a.length<=0){
              alert(123);
          }
         
      }
    </script>
</head>
<div>
    <input type="radio" name="rb" value="g"/>g
    <input type="radio" name="rb" value="h"/>h
    <input type="radio" name="rb" value="j"/>j
    <input type="radio" name="rb" value="ks"/>ks
    <button onclick="getselect()">获取选择</button>
    <button onclick="isExit()">是否存在</button>
    <div id='dv_show'>123</div>
    <button type="button" onclick="">submit</button>
    <iframe id="frm_child" src="t2.html"></iframe>
</div>

</html>